In the past, in an image forming apparatus such as a MFP (Multi Function Peripheral), if an image forming (printing) job, an operation input signal, or the like is not acquired for fixed time, control for transition to an operation mode in a power saving state in which a power supply for an image forming unit or the like including a fixing device is off, i.e., a sleep mode is performed.
However, in the sleep mode of the MFP in the past, although power supplies for the image forming unit, a display panel, and the like are turned off, processing for turning off a power supply for a CPU is not performed. This is because, if the power supply for the CPU is turned off, various kinds of processing in the image forming apparatus cannot be executed. For example, when a print job is acquired via a network, print processing cannot be executed if the power supply for the CPU is off.
Therefore, in the past, even in the sleep mode, for example, processing for suppressing power consumption is performed by keeping the power supply for the CPU on as in a normal operation mode or, instead of turning off the power supply, reducing the number of clocks of the CPU.
However, since power consumption of the CPU is relatively large, if the power supply for the CPU is kept on in the sleep mode, a sufficient power saving effect cannot be obtained. Even if the number of clocks of the CPU is reduced, the sufficient power saving effect cannot be obtained. On the other hand, if the power supply for the CPU is simply turned off, since various kinds of processing cannot be executed, functions of the MFP are limited and convenience of the MFP decreases.